Thermostatic switch calibrating device



Nov. 11, 1958 H. G. BEAR ETAL THERMOSTATIC SWITCH CALIBRATING DEVICE & m T N N 0m 5 N&m m R 4 r N L D A Mn M H M J Filed April 14, 1955 United States Patent THERMOSTATIC SWITCH CALIBRATING DEVICE Herman G. Bear, James L. Kummer, and John D. Zartman, Logansport, Ind., assignors to Essex Wire Corporation Application April 14, 1955, Serial No. 501,318

Claims. (Cl. 73-1) This invention relates to a calibration in general, but in particular to the positioning of a normally fixed electrical contact with respect to a normally moveable electrical contact.

In two-position switches, one contact is ordinarily fixed and the other moveable in response to the control influence. The fixed contact may be supported by a rigid metallic member. It is possible to calibrate such a two-position switch by'location of the moveable contact under a given control condition. In other cases, such as when the moveable contact is supported by a resilient bi-metallic strip, this type of calibration is difiicult, if not impossible. In such cases, it becomes necessary to adjust the fixed contact. This has been done, as for example, by mounting the fixed contact on a metering screw with means provided for fixing a properly adjusted screw. The primary objection to such metering devices is cost. It is most economical to use a simple metallic support and adjust the support for proper switch calibration. It is ditficult to uniformly and mechanically deform such supports for contact location, however, because of the elasticity of metallic materials or, as it is commonly termed, spring back. It is, therefore, an object of this invention to provide a device for accurately positioning an electrical contact supported by a metallic member.

In the drawings:

Fig. 1 is a plan view of a two-position switch.

Fig. 2 is a side elevation along the plane 2-2.

Fig. 3 is a side elevation partially in section of the calibrating device.

Fi 4 is an end elevation along the plane 4-4.

Fig. 5 is a plan view partially in section of the calibrating device.

Fig. 6 is a schematic illustrating of controlling circuits.

To illustrate the application of the invention reference is made to the switch indicated in Figs. 1 and 2.

The switch is a simple two-position switch with a grounded case. The switch case is constructed from a box piece 10 with lid 11. Wire terminals 12 and 13 provide the electrical connections. The contact 14 is fixed and mounted on the tang 16 which is struck from the switch casing 10. The contact is mounted on the bi-rnetal blade 17 which moves under the influence of heat to break the contacts 14 and 15.

The bi-metal blade 17 is insulated from the grounded switch casing by means of the insulating members .20 and is held in electrical engagement with termi'nal'12 by rivet 18. The casing is grounded to terminal 13 so that a circuit can be traced from terminal 12, rivet 18, oi-metal 17, contacts 14 and 15, switch casing 10, and terminal 13. Such switches are normally designed to operate at a given ambient which requires that the switch be calibrated so that the contacts remain closed up to a given ambinet and open at or above the ambient.

In order to provide a switch that will uniformly operate at the selected ambient, the switch is adjusted under base axis 21 to give the desired location of the fixed' contact 14. It is with the fast accurate adjustment of this metallic tang support 16 with respect to a second contact that this invention is concerned.

In brief, to position a metallic contact support, asindicated by tang 16, the tendency of the metal tang to spring back must be overcome. If the tang is struck or J pressed in a single progressive blow or press, release of the tool pressure causes the tang to spring back. Overriding, i. e., pressing the tang beyond the desired spot depending upon spring back to correctly locate the contact, is unreliable due to variation in response of the metal support because of variation in composition and temper. The present invention utilizes a repetitive oscillatory hammering of the metal support, combined with slow progression, to move the metal support into the desired position. The slow progression and high frequency oscillation of the metal support reduces the elasticity of the metal so that it tends to remain in position. In effect, the tendency of the metal to spring back is lessened as it is work hardened. As a result an electrical contact can be accurately located so that extremely critical switch characteristics can be achieved.

A calibrating device is illustrated in Fig. 3. The device illustrated is designed to calibrate switches to a specification calling for switch opening between 127 F. and

138 F. The machine, therefore, includes means to reject all switches which will open below 127 F. and which are closed at 138 F.

In operation, the calibrating device is loaded by means of the switch magazine 22. The switches drop into a switch guideway is shown. A strip heater 27 is used to heat a copper rail 28. Switch 29 rests on the rail 28 and is heated thereby. A glass cover 30 acts as a heat seal to prevent the loss of heat from the switches in each temperature zone. The switch moves along on the surface of rail 28 because of the pushing action of the ram 25. immediately prior to the calibrating station 31, a positioner wheel 32 is used to insure alignment of the switches. The wheel is rotated by the passing switches and the fingers 33 fit between adjacent wire terminals 12 to insure a fiat engagement of one switch against the other.

In the calibrating station 31 two actions are to be noted. In the first instance, means are provided to reciprocate a springloaded hammer at a high frequency. In addition, means are provided to move the hammer progressively downward to bend the contact support in conjunction with the oscillation of the contact support. Fig. 4 illustrates in detail the mechanical features of calibration. The switch 29 is in position under the hammer 34 so that the point of the hammer comes to rest upon actuation on the switch tang 16. The pin 35 is used to hold the switch 29 during the calibration thereof. As noted previously, it is important to obtain a high frequency flexing of the metallic contact support during the positioning thereof. This is accomplished by means o f cam 3 6 in Combination withthe compression spring 37. The 'cam 36 is revolved by any means (an air motor has been found particularly valuable because of its high starting torque) at a high-R. P. M. The hammer 34 is depressed bythe cam 36 and released by the cam shoulder 39. The'compression spring 37 forces the hammer in an upwarddire'ction each time the hammer pas es the cam shoulder 39. Dependent upon the R. P. M. of the cam wheel it can be seen that extremely high oscillation frequencies can be obtained.

In addition, the hammer 34 is concurrently moved downwardbyaction of the air cylinder 40. The piston 41 of the air cylinder is connected to the frame member 42 supporting thehammer 34. In practice it is necessary to brake 'air cylinders by the use of a check valve 43 'to set up resistance on the downward stroke of the air 'cylinderpiston .Check valves of this type are wellknown in'the art and basicallyinvolve'the useof a piston kedby a carriage 45 to the frame 42 As the pis- (on 41 is 'advanced'thepiston 44 which is linked thereto is also advanced. As the piston rod 44 is forced downward, hydraulic oil is forced ahead of its associated piston into a reservoir'through a needle valve. Such methods'of braking an air cylinder are well-known in the art and provide any desired rate of progression by adjustment of the needle valve.

The downward progress of the calibration hammer continues until'contaet is made with the moveable contact of the switch. 'Itis convenient to provide an electrical circuit through the switch for energizing the air cylinder contr01'4tla' as'a means of registering the making of the contacts and to'cause retraction of the calibrating device. After passing the calibrating station 31, the switch contacts should be closed at the ambient temperature provided, in this case 127 F. The check station 46 operates to reject thermostats which have open contacts. This is again controlled by an electrical circuit through the'switch for energizing an air cylinder control 47a. If the switch contacts are open, a knock out air cylinder 47 actuates a piston rod 48 to knock the thermostat which is outsideithe specification'through the hole 49 in the side rail 24. Following the low limit check station 46 a thermal barrier'SO. separate the low limit ambient temperature zone from the high 'limit ambient temperaturez'one. As previously discussed, a switch of this type must be open at a given high limit and in this instance the illustrative switch is required toopenbelow 138 -F. A suflicient distance is provided in the second temperature zone to permit thorough soaking of the switches to insure thatthey'are upto temperature. Ahig h limit ejector 51corresponding' in operation to the lowlimit ejector isused to reject switches with closed contacts still closed at 138 F. by means of a circuit through the switch energizing a'n aircylinder control 47b. I tacts are found to open within the specified limits, the switch is of course properly calibrated.

Having thus described our invention, we claim:

1. In apparatus for calibrating thermostatic switches wherein a metal member'carrying a normally stationary contact is displacedfor adjustment of the stationary contact relative'to a bimetal-controlled contact; a guideway in which a plurality of switches are aligned in a row for successive delivery'to a'calibratingrposition, the guideway comprising a heat insulating portion and a heated mem ber of relatively high heat conductivity in thermal con- If the switch contact with the switches for heating the switches to a 'calibrating temperature, the guideway having a cut-away portion at the calibrating position; a hammer movable in the cut-away portion of the guide way to engage the metal member of a switch located at the calibrating position for advancing the stationary contact of the switch into switching operation with the bimetal-controlled contact; means for reciprocating the hammer at a high frequency to provide a repetitive high frequency flexing of the metal member while the stationary contact is being advanced; and means responsive to switching operation of the switch contacts to cause the hammer to move away from the metal member.

2. In apparatus for calibrating thermostatic switches wherein a normally fixed contact mounted upon a metallic tang support is adjusted with respect to a movable bimetal-controlled contact; a guideway in which a plurality of switches are aligned in a row for successive delivery to a calibrating position, the guideway comprisingaheat insulating portion and aheated member of relativeIyLhigh heat conductivity in thermal contact with theswitches for heating the switches to a calibrating temperature, the guideway having a cut-away portion at the calibrating position; a hammer movable in the cut-awayportionof the guideway to engage the support of a switch located at the calibrating position for advancing the fixed contact of the switch into engagement with the bimetal-controlled contact of the switch; means forreciprocating the hammer at a high frequency toprovide a repetitive high frequency fiexing of the contact support while the fixed con tact is being advanced; and means responsive to engagement of the, switch contacts to'cause the hammer to move away from the support.

3. In apparatus, as defined in claim 2, and further characterized in that the'means for reciprocating the hammer at a high frequency comprise: a spring restraining element urging the hammer away-from the support; a cam operable to engage the hammer and to overcome the spring restraining element; and a high speed motor rotatably driving said cam to provide repeated high frequency reciprocation of the hammer during positioning of the support. a

4. In apparatus, as defined in claim 2, and further characterized in that the guideway is provided with an extension in which calibrated switches are successively delivered to a testing position Where switches having separated contacts may be ejected.-

5. In apparatus, as defined in claim 2, and further characterized in that the guideway is provided with an References Cited in the file of this patent UNITED STATES PATENTS 2,355,468 Robb Aug. 8, 1944 2,490,320 Pashby Dec. 6, 1949 2,724,961 Logue Nov. 29, 1955 V FOREIGN PATENTS 631,889 Great Britain Nov. 11, 1949 

